The present invention relates to a radio communications system, a mobile network and a base station. The invention further relates to a method for processing a radio communications system comprising a mobile network and a base station.
Radio access network solutions need to be prepared for strongly growing traffic in terms of usage, active subscribers and, in the case of emerging markets, population density. The current trends show, however, that this traffic growth is accompanied by flattening revenues of the mobile network operators. For addressing the exponential traffic growth, the operators will have to increase the density of the radio sites. While this has been proven by “V. Chandrasekhar, J. G. Andrews, and A. Gatherer, Femtocell Networks: A Survey, IEEE Communications Magazine, September 2008” to be the most effective way to increase the capacity of wireless networks, high radio sites deployment densities naturally lead to significantly increased operational expenditures. An important aspect for the future mobile network is the required capacity of backhaul links. Namely, it is not only that the increased user-generated traffic will have to be matched by the deployed backhaul links. Coupled with the traffic increase, significant overheads in transmission will emerge as well. Namely, the problem of interference barrier will become more pronounced in dense networks and solutions for interference mitigation will have to be deployed. These solutions will typically require large amounts of additional backhaul capacity as described by “P. Marsch et. al., Coordinated Multi-Point Mobile Communications, Cambridge University Press, 2011” and high investments in this area will be necessary. On the other hand, an important trend to be considered is the reduction in prices for the baseband processing hardware of radio base stations. It is expected that the form factor for the baseband processing in the small base station approaches that of a remote radio head without baseband processing (of the so called “milk bottle” size). Such a development can have a major impact on future mobile network architectures.
In contemporary radio system architectures, signal processing is completely centralized and therefore creates high costs for the optical radio site backhaul. In such systems, the backhaul traffic profile is constantly high in the area of up to 1000 times compared to end-user traffic. Additionally, it is not fluctuating over time as the end-user traffic does. This problem is exacerbated by the fact that the operators will often have to lease or share the backhaul, because fiber roll-outs are executed by incumbent operators, not necessarily the mobile network operators. The charges for this amount of capacity are unpredictable today, because the realization of the corresponding backhaul requires the deployment of next generation optical access technologies being launched in mid-term from now. Further, the radio traffic volume of the radio sites can be critical in shared medium scenarios with other services, e.g., triple play, enterprise, etc.
Today, there are two known base station or radio solution concepts for high capacity scenarios in dense urban areas which are “Distributed Base Station Architecture” and “Small Base Station Architecture”.
The Distributed Base Station concept assumes base-band pooling of radio base stations with optional radio features like, e.g., IC and joint transmission which can significantly improve the spectrum efficiency and reduce the necessary number of radio sites deployed. The layer 1/layer 2/layer 3 (L1/L2/L3) processing in the radio is placed in an extra node connected to the base stations as a so called “master”. The remote radio head includes only basic functions such as amplifiers, filters, and analog-digital conversion/digital-analog conversion functions, cf. “C-RAN, The Road Towards Green RAN”, China Mobile Research Institute White Paper, October 2011, http://labs.chinamobile.com/report/view_59826. The efficiency gain of centralized processing is strongly depending on the end-user traffic load over the day. Strong gain is only achieved in peak load hours and for small inter-site density. In other words, the gains are high typically only in interference limited situations. The DBS requires Common Public Radio Interface interfaces, cf. “Common Public Radio Interface (CPRI), Interface Specification v4.2, September 2010, http://www.cpri.info” with very high bandwidth demands for several Gbps, e.g., 30 Gbps for LTE, 20 MHz, 4×4 multiple input multiple output, 3 sectors/site. In other words, the distributed base station concept yields highest spectral efficiency at the expense of highest backhaul demands.
The small base station concept assumes a conventional small base station for all radio standards such as LTE, WiMAX, etc., and it is also related to the small cell concept specified by the Small Cell Forum “http://www.smallcellforum.org/”. The small base station concept includes namely all base station functions defined by the standards. However, its mechanical dimensions are comparable to RRH dimensions. It has much less backhaul requirements, about a factor of 20-50 less, and only line interface requirements such as Abis, IuB and S1 according to 3GPP standardization need to be fulfilled. As there is no centralized processing on lower layers, interference cancellation is less efficient than in DBS and hence spectral efficiency is lower than in the DBS case.